Connected: An Internet Encyclopedia
RFC 1510 - 6.4. Checksums

Top: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 1510
Up: 6. Encryption and Checksum Specifications
Prev: 6.3.4. DES in CBC mode with an MD5 checksum (des-cbc-md5)
Next: 6.4.1. The CRC-32 Checksum (crc32)

### 6.4. Checksums

The following is the ASN.1 definition used for a checksum:

                Checksum ::=   SEQUENCE {
                               cksumtype[0]   INTEGER,
                               checksum[1]    OCTET STRING
                }

cksumtype

  This field indicates the algorithm used to generate the accompanying checksum.

checksum

  This field contains the checksum itself, encoded as an octet string.

Detailed specification of selected checksum types appear later in this section. Negative values for the checksum type are reserved for local use. All non-negative values are reserved for officially assigned type fields and interpretations.

Checksums used by Kerberos can be classified by two properties: whether they are collision-proof, and whether they are keyed. It is infeasible to find two plaintexts which generate the same checksum value for a collision-proof checksum. A key is required to perturb or initialize the algorithm in a keyed checksum. To prevent message-stream modification by an active attacker, unkeyed checksums should only be used when the checksum and message will be subsequently encrypted (e.g., the checksums defined as part of the encryption algorithms covered earlier in this section). Collision- proof checksums can be made tamper-proof as well if the checksum value is encrypted before inclusion in a message. In such cases, the composition of the checksum and the encryption algorithm must be considered a separate checksum algorithm (e.g., RSA-MD5 encrypted using DES is a new checksum algorithm of type RSA-MD5-DES). For most keyed checksums, as well as for the encrypted forms of collisionproof checksums, Kerberos prepends a confounder before the checksum is calculated.

6.4.1. The CRC-32 Checksum (crc32)
6.4.2. The RSA MD4 Checksum (rsa-md4)
6.4.3. RSA MD4 Cryptographic Checksum Using DES (rsa-md4des)
6.4.4. The RSA MD5 Checksum (rsa-md5)
6.4.5. RSA MD5 Cryptographic Checksum Using DES (rsa-md5des)
6.4.6. DES cipher-block chained checksum (des-mac)
6.4.7. RSA MD4 Cryptographic Checksum Using DES alternative
6.4.8. DES cipher-block chained checksum alternative (desmac-k)

Next: 6.4.1. The CRC-32 Checksum (crc32)

Connected: An Internet Encyclopedia
RFC 1510 - 6.4. Checksums